feat(example): Add LP I2C Example (SHT30 temp. and humid. sensor) #4679

puyogo-suzuki · 2025-12-18T07:03:28Z

Pull Request Details 📖

Description

This PR adds an LP I2C example that reads data from an SHT30 temperature and humidity sensor.

Changes

Renamed the existing lp_core example to lp_blinky.
Moved the lp_blinky example from examples/lp_core/ to examples/lp_core/lp_blinky/.

Additions

Added a new lp_i2c example in examples/lp_core/lp_i2c/.
The LP core reads temperature and humidity from an SHT30 sensor via I2C.
Raw sensor values are converted using the formula provided in the SHT30 datasheet.
The converted values are printed to the serial console by the HP core, similar to the lp_blinky example.

Notes

I kept esp-lp-hal/example/i2c.rs, which is an old example code that uses the BMP180 sensor.
This PR is related to #4657

Testing

I tested the renamed lp_blinky example and the new lp_i2c example with the following environment:

OS: Debian 13
Rust ver.: 1.94-nightly
Board: ESP32-C6-Devkit-C
Sensor: SHT30 (M5Stack ENV-II)

Submission Checklist 📝

I have updated existing examples or added new ones (if applicable).
I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
My changes were added to the CHANGELOG.md in the proper section.
I have added necessary changes to user code to the latest Migration Guide.
My changes are in accordance to the esp-rs developer guidelines

Extra:

I have read the CONTRIBUTING.md guide and followed its instructions.

Copilot

Pull request overview

This PR adds a new LP I2C example demonstrating communication with an SHT30 temperature and humidity sensor, and reorganizes the existing LP core examples by moving them into subdirectories.

Key Changes

Renamed and relocated the existing lp_core example to lp_core/lp_blinky/ with updated relative paths
Added a new lp_i2c example that reads temperature and humidity data from an SHT30 sensor via the LP core's I2C peripheral
Created corresponding LP core code in esp-lp-hal/examples/i2c_sht30.rs that performs the actual sensor reading

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
examples/peripheral/lp_core/lp_i2c/src/main.rs	New HP core example that initializes LP I2C and displays sensor readings
examples/peripheral/lp_core/lp_i2c/Cargo.toml	Dependencies and configuration for the new lp_i2c example
examples/peripheral/lp_core/lp_i2c/.cargo/config.toml	Build configuration for the new example
examples/peripheral/lp_core/lp_blinky/src/main.rs	Updated path reference after directory restructuring
examples/peripheral/lp_core/lp_blinky/Cargo.toml	New dependency paths reflecting the directory structure change
examples/peripheral/lp_core/lp_blinky/.cargo/config.toml	Build configuration moved with the example
esp-lp-hal/examples/i2c_sht30.rs	New LP core code that reads SHT30 sensor data and writes to shared memory
esp-lp-hal/Cargo.toml	Added the new i2c_sht30 example definition

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Copilot · 2025-12-18T07:16:19Z

esp-lp-hal/examples/i2c_sht30.rs

+#![no_std]
+#![no_main]
+
+use embedded_hal::delay::DelayNs;


The import embedded_hal::delay::DelayNs is unused. The code only uses Delay.delay_ms() which comes from the esp_lp_hal::delay::Delay import and its trait implementation, not from this DelayNs trait import.

Suggested change

use embedded_hal::delay::DelayNs;

Delay.delay_ms comes from embedded_hal::delay::DelayNs.
Thus, it is necessary.

examples/peripheral/lp_core/lp_i2c/src/main.rs

esp-lp-hal/Cargo.toml

Copilot · 2025-12-18T07:16:20Z

esp-lp-hal/examples/i2c_sht30.rs

+fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {
+    let mut buffer = [0u8; 6];
+    i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;
+    let temp_raw = u16::from_be_bytes([buffer[0], buffer[1]]);
+    let hum_raw = u16::from_be_bytes([buffer[3], buffer[4]]);
+    let temperature = -45.0 + (175.0 * (temp_raw as f32) / 65535.0);
+    let humidity = 100.0 * (hum_raw as f32) / 65535.0;
+    Ok((temperature, humidity))


The SHT30 sensor data includes CRC bytes at positions [2] and [5] of the buffer which are currently being ignored. According to the SHT30 datasheet, the sensor sends 6 bytes: 2 bytes temp data, 1 byte CRC, 2 bytes humidity data, 1 byte CRC. Not validating these CRC values means corrupted sensor readings could be silently accepted and displayed as valid data.

Suggested change

fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {

let mut buffer = [0u8; 6];

i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;

let temp_raw = u16::from_be_bytes([buffer[0], buffer[1]]);

let hum_raw = u16::from_be_bytes([buffer[3], buffer[4]]);

let temperature = -45.0 + (175.0 * (temp_raw as f32) / 65535.0);

let humidity = 100.0 * (hum_raw as f32) / 65535.0;

Ok((temperature, humidity))

/// Calculate CRC for SHT30 two-byte data using polynomial 0x31 and initial value 0xFF.

fn sht30_crc(data: &[u8]) -> u8 {

let mut crc: u8 = 0xFF;

for byte in data {

crc ^= *byte;

for _ in 0..8 {

if (crc & 0x80) != 0 {

crc = (crc << 1) ^ 0x31;

} else {

crc <<= 1;

}

}

}

crc

}

fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {

let mut buffer = [0u8; 6];

loop {

// Read 2 bytes temperature, 1 byte CRC, 2 bytes humidity, 1 byte CRC.

i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;

let temp_data = [buffer[0], buffer[1]];

let temp_crc = buffer[2];

let hum_data = [buffer[3], buffer[4]];

let hum_crc = buffer[5];

if sht30_crc(&temp_data) == temp_crc && sht30_crc(&hum_data) == hum_crc {

let temp_raw = u16::from_be_bytes(temp_data);

let hum_raw = u16::from_be_bytes(hum_data);

let temperature = -45.0 + (175.0 * (temp_raw as f32) / 65535.0);

let humidity = 100.0 * (hum_raw as f32) / 65535.0;

return Ok((temperature, humidity));

}

// If CRC check fails, repeat the measurement instead of returning corrupted data.

}

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated 8 comments.

Comments suppressed due to low confidence (1)

examples/peripheral/lp_core/lp_i2c/Cargo.toml:2

The package name "lp-core-i2c" should likely be more specific, such as "lp-core-i2c-sht30", to distinguish it from the generic "lp-core-blinky" pattern and to match the example's specific sensor usage.

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Copilot · 2025-12-18T07:50:09Z

esp-lp-hal/examples/i2c_sht30.rs

+
+use embedded_hal::delay::DelayNs;
+use esp_lp_hal::{
+    delay::Delay,


The Delay import is unused in this code. The code uses Delay.delay_ms(1000) which creates a Delay instance inline. Consider either removing the import or storing the Delay instance as a variable for clarity.

Both esp_lp_hal::delay::Delay and embedded_hal::delay::DelayNs are necessary.
Removing either leads to an compilation error.

esp-lp-hal/examples/i2c_sht30.rs

examples/peripheral/lp_core/lp_i2c/.cargo/config.toml

esp-lp-hal/examples/i2c_sht30.rs

Copilot · 2025-12-18T07:50:10Z

esp-lp-hal/examples/i2c_sht30.rs

+
+fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {
+    let mut buffer = [0u8; 6];
+    i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;


The SHT30 sensor returns a 6-byte response where bytes 2 and 5 are CRC checksums for the temperature and humidity data respectively. This code reads the CRC bytes but does not validate them, which could result in displaying corrupted sensor readings. Consider adding CRC validation to ensure data integrity.

Suggested change

fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {

let mut buffer = [0u8; 6];

i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;

/// Compute CRC-8 for SHT3x (polynomial 0x31, initial value 0xFF) over a 2-byte word.

fn crc8_sht(data: &[u8]) -> u8 {

let mut crc: u8 = 0xFF;

for &byte in data {

crc ^= byte;

for _ in 0..8 {

if (crc & 0x80) != 0 {

crc = (crc << 1) ^ 0x31;

} else {

crc <<= 1;

}

}

}

crc

}

fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {

let mut buffer = [0u8; 6];

i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;

// Validate CRC for temperature (bytes 0-1, CRC at byte 2)

let temp_crc_calc = crc8_sht(&buffer[0..2]);

if temp_crc_calc != buffer[2] {

return Err(Error::Bus);

}

// Validate CRC for humidity (bytes 3-4, CRC at byte 5)

let hum_crc_calc = crc8_sht(&buffer[3..5]);

if hum_crc_calc != buffer[5] {

return Err(Error::Bus);

}

esp-lp-hal/examples/i2c_sht30.rs

examples/peripheral/lp_core/lp_i2c/src/main.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated 3 comments.

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examples/peripheral/lp_core/lp_i2c/src/main.rs

Copilot · 2025-12-22T04:37:33Z

esp-lp-hal/examples/i2c_sht30.rs

+    let temp_raw = u16::from_be_bytes([buffer[0], buffer[1]]);
+    let hum_raw = u16::from_be_bytes([buffer[3], buffer[4]]);


The SHT30 sensor returns CRC checksums at buffer[2] and buffer[5] that should be validated to ensure data integrity. The datasheet specifies that each data word (temperature and humidity) is followed by an 8-bit CRC. Skipping CRC validation could result in processing corrupted sensor data. Consider adding CRC validation or documenting why it's intentionally omitted.

esp-lp-hal/examples/i2c_sht30.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated 3 comments.

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examples/peripheral/lp_core/lp_i2c/src/main.rs

Copilot · 2025-12-22T04:45:04Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+            unsafe { temp.read_volatile() },
+            unsafe { humid.read_volatile() }


Reading temperature and humidity values separately with two volatile reads could result in reading inconsistent data if the LP core updates the values between the two reads. The HP core might read a temperature from one sensor reading cycle and humidity from another. Consider adding a comment documenting this potential race condition, or reading both values atomically if data consistency is critical.

esp-lp-hal/examples/i2c_sht30.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

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esp-lp-hal/examples/i2c_sht30.rs

Copilot

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

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Copilot · 2025-12-22T06:02:42Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+    let humid = HUMID_ADDRESS as *mut f32;
+    loop {
+        print!(
+            "Current {:.2} C {:.2} %           \u{000d}",


The temperature unit display should use the degree symbol (°C) instead of just "C" for better readability and to follow standard notation for temperature measurements. Consider changing the format string to include the degree symbol.

Suggested change

"Current {:.2} C {:.2} % \u{000d}",

"Current {:.2} °C {:.2} % \u{000d}",

esp-lp-hal/examples/i2c_sht30.rs

puyogo-suzuki · 2025-12-22T06:39:28Z

I have accepted the following suggestions from Copilot:

Added comments for clarity.
Updated the error handling logic.
Used i2c.write, delay, and i2c.read instead of i2c.write_read.

However, I disagree with these suggestions:

Adding a CRC check.
Adding a comment regarding a potential race condition.
Changing "C" to "°C" when printing values.

Since this is intended as a simple example for LPI2C, I believe it is better to keep the code minimal and concise.
Do you think I should accept these remaining suggestions?

SergioGasquez

Changes lgtm and I think the new example is a great addition! I couldnt test it as I dont have SHT30 though

I guess in the future we could improve the experience of running lp examples and make the xtask build the lp example, but thats for another PR!

Copilot

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 6 comments.

Comments suppressed due to low confidence (1)

examples/peripheral/lp_core/lp_i2c/Cargo.toml:21

Missing esp-println chip feature in the esp32c6 feature list. The esp-println dependency should include "esp-println/esp32c6" in the features array, consistent with other examples in the repository. This ensures esp-println is properly configured for the target chip.

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Copilot · 2025-12-22T15:10:01Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+    let i2c = LpI2c::new(
+        peripherals.LP_I2C0,
+        LowPowerOutputOpenDrain::new(peripherals.GPIO6),
+        LowPowerOutputOpenDrain::new(peripherals.GPIO7),
+        Rate::from_khz(100),
+    );


The i2c variable is created but its name is misleading. While it appears unused in the HP core's main function, it is actually consumed and transferred to the LP core via the lp_core_code.run() call. Consider renaming it to lp_i2c to make it clearer that this I2C instance is intended for the LP core, improving code readability.

I disagree this because we don't use the HP I2C controller.
The naming i2c is not confusing.

Copilot · 2025-12-22T15:10:02Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+        print!(
+            "Current {:.2} C {:.2} %           \u{000d}",
+            unsafe { temp.read_volatile() },
+            unsafe { humid.read_volatile() }


The HP core continuously reads shared memory values written by the LP core without any synchronization mechanism. This creates a potential race condition where the HP core could read a partially updated value if it reads in the middle of the LP core's write operation. While f32 writes might be atomic on some architectures, this is not guaranteed. Consider using atomic operations or adding a synchronization mechanism (like a flag or sequence number) to ensure the HP core reads consistent data.

Suggested change

print!(

"Current {:.2} C {:.2} % \u{000d}",

unsafe { temp.read_volatile() },

unsafe { humid.read_volatile() }

// Take a consistent snapshot of temperature and humidity.

// We read temperature, then humidity, then temperature again.

// If both temperature reads match bit-for-bit, we assume the LP core

// was not in the middle of updating the values and print the pair.

let (t, h) = loop {

let t1 = unsafe { temp.read_volatile() };

let h = unsafe { humid.read_volatile() };

let t2 = unsafe { temp.read_volatile() };

if t1.to_bits() == t2.to_bits() {

break (t1, h);

}

// Otherwise, try again until we get a stable snapshot.

};

print!(

"Current {:.2} C {:.2} % \u{000d}",

t,

h

This is just a simple example.
We don't need to think about a potential race condition.

Copilot · 2025-12-22T15:10:02Z

examples/peripheral/lp_core/lp_blinky/Cargo.toml

+esp32c6 = [
+    "esp-backtrace/esp32c6",
+    "esp-bootloader-esp-idf/esp32c6",
+    "esp-hal/esp32c6",


Missing esp-println chip feature in the esp32c6 feature list. The esp-println dependency should include "esp-println/esp32c6" in the features array, consistent with other examples in the repository. This ensures esp-println is properly configured for the target chip.

Suggested change

"esp-hal/esp32c6",

"esp-hal/esp32c6",

"esp-println/esp32c6",

It seems that only examples/async/embassy_hello_world_defmt enables it.

Copilot · 2025-12-22T15:10:03Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+    loop {
+        print!(
+            "Current {:.2} C {:.2} %           \u{000d}",
+            unsafe { temp.read_volatile() },
+            unsafe { humid.read_volatile() }
+        );
+    }


The infinite loop continuously reads and prints sensor values without any delay, which will consume 100% CPU on the HP core. Consider adding a small delay between iterations to reduce CPU usage and power consumption, especially since the LP core only updates the values every 1000ms.

This is just a simple example!

Copilot · 2025-12-22T15:10:03Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+        print!(
+            "Current {:.2} C {:.2} %           \u{000d}",
+            unsafe { temp.read_volatile() },
+            unsafe { humid.read_volatile() }
+        );


The format string uses \u{000d} (carriage return) to overwrite the line. Consider adding a comment explaining this behavior, as it creates an updating display rather than scrolling output. This would help developers understand why the carriage return is used instead of a newline.

This follows the lp_blinky example.

Copilot · 2025-12-22T15:10:03Z

examples/peripheral/lp_core/lp_i2c/src/main.rs

+    let humid = HUMID_ADDRESS as *mut f32;
+    loop {
+        print!(
+            "Current {:.2} C {:.2} %           \u{000d}",
+            unsafe { temp.read_volatile() },
+            unsafe { humid.read_volatile() }


Variable naming is inconsistent between the HP and LP cores. The HP core uses humid while the LP core uses hum_ptr and hum_raw. Consider using consistent naming across both cores (either humid or humidity throughout) to improve code maintainability and make the relationship between the cores clearer.

Suggested change

let humid = HUMID_ADDRESS as *mut f32;

loop {

print!(

"Current {:.2} C {:.2} % \u{000d}",

unsafe { temp.read_volatile() },

unsafe { humid.read_volatile() }

let hum_ptr = HUMID_ADDRESS as *mut f32;

loop {

print!(

"Current {:.2} C {:.2} % \u{000d}",

unsafe { temp.read_volatile() },

unsafe { hum_ptr.read_volatile() }

I do not think that this naming is confusing.

puyogo-suzuki · 2025-12-22T15:30:07Z

Thanks @SergioGasquez
I’ve retested it on the actual hardware and it works as expected.
I don't think we need to apply further suggestions from Copilot for now.

I've completed everything on my end.

SergioGasquez

Thanks!

feat(example): Add LP I2C Example (SHT30 temp. and humid. sensor)

993a990

Copilot AI review requested due to automatic review settings December 18, 2025 07:03

puyogo-suzuki mentioned this pull request Dec 18, 2025

Proposal: Adding an LP I2C Example (using SHT30) #4657

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Fix the wrong attribute name required_features in Cargo.toml.

19b42f7

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Copilot AI review requested due to automatic review settings December 18, 2025 07:44

Fix file name.

dc6f427

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MabezDev added the skip-changelog No changelog modification needed label Dec 19, 2025

Added descriptions for constants.

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puyogo-suzuki and others added 2 commits December 22, 2025 13:39

Added some spaces.

91bb151

Split write and read.

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Added descriptions for addresses.

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Added descriptions for addresses on main.

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esp-lp-hal/examples/i2c_sht30.rs Outdated Show resolved Hide resolved

puyogo-suzuki added 2 commits December 22, 2025 14:16

Changed I2C failure handling.

0434643

Fix link.

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Change the variable name

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Merge branch 'main' into feat/example_lp_i2c_sht30

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SergioGasquez added this pull request to the merge queue Dec 23, 2025

Merged via the queue into esp-rs:main with commit 6b735e1 Dec 23, 2025
30 checks passed

-fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {
-    let mut buffer = [0u8; 6];
-    i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;
-    let temp_raw = u16::from_be_bytes([buffer[0], buffer[1]]);
-    let hum_raw = u16::from_be_bytes([buffer[3], buffer[4]]);
-    let temperature = -45.0 + (175.0 * (temp_raw as f32) / 65535.0);
-    let humidity = 100.0 * (hum_raw as f32) / 65535.0;
-    Ok((temperature, humidity))
+/// Calculate CRC for SHT30 two-byte data using polynomial 0x31 and initial value 0xFF.
+fn sht30_crc(data: &[u8]) -> u8 {
+    let mut crc: u8 = 0xFF;
+    for byte in data {
+        crc ^= *byte;
+        for _ in 0..8 {
+            if (crc & 0x80) != 0 {
+                crc = (crc << 1) ^ 0x31;
+            } else {
+                crc <<= 1;
+            }
+        }
+    }
+    crc
+}
+fn read_temp_humid(i2c: &mut LpI2c) -> Result<(f32, f32), Error> {
+    let mut buffer = [0u8; 6];
+    loop {
+        // Read 2 bytes temperature, 1 byte CRC, 2 bytes humidity, 1 byte CRC.
+        i2c.write_read(DEV_ADDR, &CMD_READ_ONESHOT, &mut buffer)?;
+        let temp_data = [buffer[0], buffer[1]];
+        let temp_crc = buffer[2];
+        let hum_data = [buffer[3], buffer[4]];
+        let hum_crc = buffer[5];
+        if sht30_crc(&temp_data) == temp_crc && sht30_crc(&hum_data) == hum_crc {
+            let temp_raw = u16::from_be_bytes(temp_data);
+            let hum_raw = u16::from_be_bytes(hum_data);
+            let temperature = -45.0 + (175.0 * (temp_raw as f32) / 65535.0);
+            let humidity = 100.0 * (hum_raw as f32) / 65535.0;
+            return Ok((temperature, humidity));
+        }
+        // If CRC check fails, repeat the measurement instead of returning corrupted data.
+    }

		let temp_raw = u16::from_be_bytes([buffer[0], buffer[1]]);
		let hum_raw = u16::from_be_bytes([buffer[3], buffer[4]]);

		unsafe { temp.read_volatile() },
		unsafe { humid.read_volatile() }

	"Current {:.2} C {:.2} % \u{000d}",
	"Current {:.2} °C {:.2} % \u{000d}",

-        print!(
-            "Current {:.2} C {:.2} %           \u{000d}",
-            unsafe { temp.read_volatile() },
-            unsafe { humid.read_volatile() }
+        // Take a consistent snapshot of temperature and humidity.
+        // We read temperature, then humidity, then temperature again.
+        // If both temperature reads match bit-for-bit, we assume the LP core
+        // was not in the middle of updating the values and print the pair.
+        let (t, h) = loop {
+            let t1 = unsafe { temp.read_volatile() };
+            let h = unsafe { humid.read_volatile() };
+            let t2 = unsafe { temp.read_volatile() };
+            if t1.to_bits() == t2.to_bits() {
+                break (t1, h);
+            }
+            // Otherwise, try again until we get a stable snapshot.
+        };
+        print!(
+            "Current {:.2} C {:.2} %           \u{000d}",
+            t,
+            h

feat(example): Add LP I2C Example (SHT30 temp. and humid. sensor) #4679

feat(example): Add LP I2C Example (SHT30 temp. and humid. sensor) #4679

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puyogo-suzuki commented Dec 18, 2025

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puyogo-suzuki commented Dec 22, 2025

puyogo-suzuki Dec 22, 2025 •

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